Systems and methods for improving the efficiency of a power plant exploit the temperature differential of the cooling water that may exist seasonally in some geographic locations. Specifically, new systems and ways of retrofitting existing systems to utilize the additional temperature differential of a power plant's coolant during colder months are provided in order to increase the efficiency of the plant. A second working fluid loop converts a portion of the condenser of the first working fluid loop into the boiler for the second working fluid loop in which the first and second working fluids in these respective loops are different. Thus, the energy output of the plant may be increased by the addition of a selectively operated secondary loop without an increase in fuel consumption.